The conventional roller type conveyers used to carry materials in factories usually have the following disadvantages:
1. They are built in a straight line only, being unable to operate along a curved line.
2. The space between two rollers can not be changed to accomodate the sizes of materials to be conveyed.
3. Since the rollers are set up horizontally at a fixed height, it is difficult to set up them over a rugged ground.
4. They cannot carry cylindrical materials, as there is no channel-like rollers to hold the cylindrical materials or objects.